The invention relates to an information recording medium which is used as an optical disk.
Various principles for recording information onto a thin film (recording film) by irradiating a laser beam are known. Among them, since the principle using an atomic arrangement change due to the irradiation of a laser beam such as phase transition (also called a phase change) of a film material, photodarkening, or the like is hardly accompanied with deformation of a thin film, it has a merit such that an information recording medium of a double-sided disk structure is obtained by directly adhering two disk materials. A recording film of a GeSbTe system or the like has an advantage such that information can be rewritten.
According to such a kind of recording film, however, if a mark edge recording or the like to realize a high density is performed, since erasing characteristics are insufficient, a film thickness of the recording film changes due to a flow of the recording film because of a deterioration of jitter due to the rewriting or the rewriting of a number of times exceeding 104, so that a distortion occurs in a reproduction signal waveform. The flow of the recording film occurs by the reason that the recording film flows by the laser irradiation upon recording and the recording film is pressed little by little due to a deformation of a protection layer or an intermediate layer by a thermal expansion. The mark edge recording is a recording system such that an edge portion of a recording mark is made correspond to xe2x80x9c1xe2x80x9d of a signal and a portion between the marks and a portion in the mark are made correspond to xe2x80x9c0xe2x80x9d.
For example, a method whereby a heat capacity is reduced by thinning the recording film and a flow of the recording film is prevented by using a principle such that an influence by an adhesion between the recording film and an adjacent layer increases has been disclosed in a literature 1, xe2x80x9cT. Ohta et al., xe2x80x9cOptical Data Storagexe2x80x9d, ""89 Proc. SPIE, 1078, 27 (1989)xe2x80x9d. A method whereby a component of a high melting point is added into a recording film and a flow of the recording film is prevented has been disclosed in a literature 2, xe2x80x9cHirotsune, Terao, Miyauchi, Minemura, and Fushimi, the Record, p1000, of the 41st Meeting of Applied Physics Concerned Associationxe2x80x9d. Thus, the large flow of the recording film could be suppressed. However, if the rewriting of a number of times is further repeated, a fluctuation in reflectance level occurs.
To improve overwrite jitter characteristics in the mark edge recording, a disk in which transmitted light is increased has been proposed in a literature 3, xe2x80x9cOkubo, Murabatake, Ide, Okada, and Iwanaga, the Record, p98, of the 5th Meeting of the Society of Research of Phase Change Recordingxe2x80x9d. The disk is constructed by a PC substrate/ZnSxe2x88x92SiO2 (250 nm)/Ge2Sb2Te5 (15 nm)/ZnSxe2x88x92SiO2 (18 nm)/Si (65 nm).
In JP-A-8-329525, the applicant of the present invention has already disclosed the invention in which a reflection layer is constructed by two layers, a material of the reflection layer is a combination of Al and Si, and a refractive index and an attenuation coefficient of the reflection layer are specified.
Although not become prior art yet, in Japanese Patent Application No. 8-328183 (1996), the applicant of the present invention has already disclosed that Al and the like are used as main components of a first metal layer and a second metal layer and a content of Al and the like of the second metal layer is set to be larger than that of Al and the like of the first metal layer provided near a recording film.
In the specification, a term of xe2x80x9cphase change,xe2x80x9d is used as a word including not only the phase change between crystalxe2x80x94amorphous but also a phase change between a fusion (change to a liquid phase) and a recrystallization and a phase change between a crystal statexe2x80x94a crystal state.
Any of the conventional information recording media has a problem such that in case of using it as a rewritable information recording medium of a phase transition type of a high density using the mark edge recording, an increase in jitter due to the rewriting, an increase in jitter at the time of rewriting of a number of times, and a fluctuation in reflectance level occur because erasing characteristics are insufficient.
It is, therefore, an object of the invention to provide an information recording medium in which even if the rewriting is executed or the rewriting is executed a number of times, preferable recording and reproducing characteristics are held, an increase in jitter is smaller, and a fluctuation of a reflectance level is smaller than those of a conventional medium.
(1) The medium of the invention is characterized in that it has a structure such that an information recording thin film which is formed on a substrate and records and/or reproduces information by an atomic arrangement change which occurs by receiving an irradiation of light is provided as a recording layer, at least one protection layer is provided, the protection layer and recording layer are laminated in order from the light incident side, and at least one reflection layer is subsequently laminated through at least one intermediate layer, the recording layer satisfies
Gexxe2x88x92wSbyTezMw
and lies within a range which satisfies
0.13xe2x89xa6xxe2x89xa60.22, 0.20 xe2x89xa6yxe2x89xa60.32,
0.53xe2x89xa6zxe2x89xa60.60, wxe2x89xa60.06, and x+y+z=1
and M consists of any one of
Na, Mg, Al, P, S, Cl, K, Ca, Sc, Zn, Ga, As, Se, Br, Rb, Sr, Y, Zr, Nb, Ru, Rh, Cd, In, Sn, I, Cs, Ba, La, Hf, Ta, Re, Os, Ir, Hg, Tl, Pb, Th, U, Ag, Cr, W, Mo, Pt, Co, Ni, Pd, Si, Au, Cu, V, Mn, Fe, Ti, and Bi.
(2) The information recording medium according to (1) is characterized in that the reflection layer comprises a first reflection layer and a second reflection layer which are made of materials of different compositions.
(3) The information recording medium according to (1) is characterized in that the reflection layer comprises a first reflection layer and a second reflection layer which are made of materials in which at least ones of refractive indices or attenuation coefficients are different.
(4) The information recording medium according to any one of (1) to (3) is characterized in that the M is at least one element selected from a group including Ag, Cr, W, and Mo.
(5) The information recording medium according to any one of (1) to (3) is characterized in that the M is at least one element selected from a group including Pd, Pt, and Co.
(6) The information recording medium according to any one of (1) to (5) is characterized in that the protection layer includes a layer containing ZnS of 70 mol % or ore.
(7) The information recording medium according to any one of (1) to (5) is characterized in that the protection layer has a layer of a composition in which at least 90% or more of the total number of atoms is close to any one of (ZnS)xe2x80x94(SiO2), (ZnS)xe2x80x94(Al2O3), (ZnS)xe2x80x94(Al2O3)xe2x80x94(SiO2), and (ZnS)xe2x80x94(Ta2O5) or a mixture composition thereof.
(8) The information recording medium according to any one of (1) to (5) is characterized in that the protection layer has a layer made of a material containing Alxe2x80x94O of 70 mol % or more.
(9) The information recording medium according to any one of (1) to (5) is characterized in that the protection layer includes two layers made of materials of different compositions.
(10) The information recording medium according to any one of (1) to (5) is characterized in that the protection layer includes at least two layers of a film containing ZnS of 70 mol % or more and a film containing Alxe2x80x94O or Sixe2x80x94O of 70 mol % or more.
(11) The information recording medium according to any one of (1) to (5) is characterized in that the protection layer includes a film containing at least one of Alxe2x80x94O and Sixe2x80x94O of 70 mol % or more is provided between the film containing ZnS of 70 mol % or more and the recording film.
(12) The information recording medium according to (2) or (3) is characterized in that a component of 95% or more of the total number of atoms of the first reflection layer includes an Al alloy.
(13) The information recording medium according to (2) or (3) is characterized in that a component of 95% or more of the total number of atoms of the second reflection layer includes an Al alloy.
(14) The information recording medium according to (2) or (3) is characterized in that both the first reflection layer and the second reflection layer contain 95% or more of the total number of atoms of Al or an Al alloy, and a content of elements other than Al of the first reflection layer is larger than a content of elements other than Al of the second reflection layer.
(15) The information recording medium according to (2) or (3) is characterized in that the refractive index of the first reflection layer is larger than the refractive index of the second reflection layer, and the attenuation coefficient of the first reflection layer is smaller than the attenuation coefficient of the second reflection layer.
(16) The information recording medium according to (2) or (3) is characterized in that a component of 80% or more of the total number of atoms of the first reflection layer includes Si.
(17) The information recording medium according to (2) or (3) is characterized in that a component of 95% or more of the total number of atoms of the first reflection layer includes Si or a mixture or compound of Si and a metal element, and a component of 95% or more of the total number of atoms of the second reflection layer including an Al alloy.
(18) The information recording medium according to any one of (1) to (5) is characterized in that the intermediate layer includes a layer containing ZnS of 70 mol % or more.
(19) The information recording medium according to any one of (1) to (5) is characterized in that the intermediate layer has a layer of a composition in which 90% or more of the total number of atoms is close to any one of (ZnS)xe2x80x94(Al2O3), (ZnS)xe2x80x94(SiO2), SiO2, (Al2O3), and (ZnS)xe2x80x94(Al2O3)xe2x80x94(SiO2) or a mixture composition thereof.
(20) The information recording medium according to any one of (1) to (5) is characterized in that the intermediate layer has a layer made of a material containing Alxe2x80x94O of 70 mol % or more.
(21) The information recording medium according to any one of (1) to (5) is characterized in that the intermediate layer includes two layers made of materials of different compositions.
(22) The information recording medium according to any one of (1) to (5) is characterized in that the intermediate layer includes at least two layers of a film containing ZnS of 70 mol % or more and a film containing at least one of Alxe2x80x94O and Sixe2x80x94O of 70 mol % or more.
(23) The information recording medium according to any one of (1) to (5) is characterized in that a film thickness of the recording film lies within a range of 10 nm or more and 30 nm or less.
(24) The information recording medium according to any one of (1) to (5) is characterized in that a film thickness of the protection layer lies within a range of 80 nm or more and 110 nm or less.
(25) The information recording medium according to any one of (1) to (5) is characterized in that a film thickness of the intermediate layer lies within a range of 10 nm or more and 30 nm or less.
(26) The information recording medium according to any one of (1) to (5) is characterized in that a film thickness of the reflection layer lies within a range of 80 nm or more and 240 nm or less.
(27) The information recording medium according to (2) or (3) is characterized in that a film thickness of the first reflection layer lies within a range of 40 nm or more and 120 nm or less.
(28) The information recording medium according to (2) or (3) is characterized in that a film thickness of the second reflection layer lies within a range of 40 nm or more and 120 nm or less.
(29) An information recording medium characterized in that an information recording thin film which is formed on a substrate and records and/or reproduces information by an atomic arrangement change which occurs by receiving an irradiation of light is provided as a recording film, a reflection layer is provided, and a reflectance change of a crystal state and/or an amorphous state is equal to or less than 5% within a wavelength range of xc2x150 nm or less around a wavelength adapted to record and/or reproduce as a center.
(30) An information recording medium characterized in that an information recording thin film which is formed on substrate and records and/or reproduces information by an atomic arrangement change which occurs by receiving an irradiation of light is provided as a recording film, an intermediate layer and a reflection layer are provided, and when separating into two layers at a boundary face between the recording film and the intermediate layer, a reflectance change of the reflection layer at a timing when the light enters from the intermediate layer side through the intermediate layer is equal to or less than 5% within a wavelength range of xc2x150 nm or less around a wavelength adapted to record and/or reproduce as a center.
(31) An information recording medium characterized in that an information recording thin film which is formed on a substrate and records and/or reproduces information by an atomic arrangement change which occurs by receiving an irradiation of light is provided as a recording film, an intermediate layer and a reflection layer are provided, and a reflectance of the protection layer at a timing when separating into two layers at a boundary face between the recording film and the intermediate layer when the light enters from the recording film side through the recording film has a minimal value within a wavelength range from a wavelength that is shorter than a wavelength adapted to record and/or reproduce by 200 nm to a wavelength that is shorter than such a wavelength by 100 nm.
(32) In the recording film, it is more preferable that a range of x satisfies (0.15xe2x89xa6xxe2x89xa60.20), it is more preferable that a range of y satisfies (0.22xe2x89xa6yxe2x89xa60.30), and it is more preferable that a range of z satisfies (0.54xe2x89xa6zxe2x89xa60.58).
It is preferable that a content of impurity elements in the recording film is equal to or less than 5 atom % of the recording film component because a deterioration of rewriting characteristics can be reduced. It is further preferable that the content is equal to or less than 2 atom %.
It is preferable that the film thickness of the recording film is equal to 10 nm or more and is equal to 30 nm or less, more preferably, is equal to 13 nm or more and is equal to 20 nm or less.
(33) It is preferable that a mol ratio of ZnS in (ZnS)xe2x80x94(SiO2) of the first protection layer is equal to 70 mol % or more and 90 mol % or less.
The first protection layer is characterized in that it includes (ZnS)80(SiO2)20. As a material which is substituted for (ZnS)80(SiO2)20, it is possible to use an Sixe2x80x94N system material, an Sixe2x80x94Oxe2x80x94N system material, an oxide such as SiO2, SiO, TiO2, Al2O3, Y2O3, CeO2, La2O3, In2O3, GeO, GeO2PbO, SnO, SnO2, BeO, Bi2O3, TeO2, WO2, WO3, Sc2O3, Ta2O5, ZrO2, Cu2O, MgO, or the like, a nitride such as TaN, AlN, BN, Si3N4, GeN, Alxe2x80x94Sixe2x80x94N system material (for example, AlSiN2), or the like, a sulfide such as ZnS, Sb2S3, CdS, In2S3, Ga2S3, GeS, SnS2, PbS, Bi2Se3, or the like, a selenide such as SnSe2, Sb2Se3, CdSe, ZnSe, In2Se3, Ga2Se3, GeSe, GeSe2, SnSe, PbSe, Bi2Se3, or the like, a fluoride such as CeF3, MgF2, CaF2or the like, Si, Ge, TiB2, B4C, B, C, or a material made of a composition close to the above materials. A layer of those mixture materials or a multilayer of them can be used.
The second protection layer is characterized in that it includes Al2O3. As a material which is substituted for Al2O3, SiO2 or a mixture of Al203 and SiO2 is preferable. If SiO2 or Al2O3 of 70 atom % or more is contained, a reduction of the reflectance level due to the rewriting of 100,000 times is small and can be suppressed to 5% or less. If SiO2 or Al2O3 of 90 atom % or more is contained, it can be suppressed to 3% or less. As a material which is substituted for Al2O3 of a second protection layer 3, Ta2O5 is subsequently preferable and ZrO2xe2x80x94Y2O3 is subsequently preferable. In place of Al2O3 of the second protection layer, if a Crxe2x80x94O system material such as Cr2O3, CrO, or the like, a Coxe2x80x94O system material such as Co2O3, CoO, or the like, a material of a composition close to them, or a mixture material of them is used, it is preferable because an adhesive strength between the protection layer and the recording film is strong. An Nixe2x80x94O system material or a mixture material of them can be used.
It is desirable to use a nitride such as Gexe2x80x94N, Sixe2x80x94N, or Alxe2x80x94N system material besides them because there is an effect such that a crystallization speed rises and an unerased remainder at a high linear velocity decreases. Even in case of forming by adding nitrogen into the recording film material, the crystallization speed rises.
In the case where the protection layer includes two or more layers of different materials as mentioned above, although the number of manufacturing steps increases, it is preferable because there are both effects such that an increase in noises is prevented and a diffusion of the protection layer material into the recording film is prevented.
As combinations of the first and second protection layers, (ZnS)80(SiO2)20 and Al2O3 are preferable because the reflectance level change upon rewriting is small to be 3% or less. In case of (ZnS)80(SiO2)20 and SiO2, a DC erasing ratio is equal to 30 dB and preferable erasing characteristics are obtained. A combination of ZnS and any one of SiO2, Al2O3, and Ta2O5 is preferable because a modulation degree is large to be 53% or more.
It is preferable that an element ratio in those compounds is equal to a ratio of a metal element and an oxygen element, for example, in the oxide or sulfide or with respect to the metal element and the sulfide element, it is equal to a ratio of 2:3 in case of Al2O3, Y2O3, and La2O3, 1:2 in case of SiO2, ZrO2, and GeO2, 2:5 in case of Ta2O5, or 1:1 in case of ZnS or a ratio close to it. However, even if the ratio is out of such a ratio, similar effects are obtained. When the ratio is out of the above integer ratio, it is preferable that the deviation of the metal element amount is equal to or less than 10%, namely, for example, the ratio of Al and O in case of Alxe2x80x94O is equal to xc2x110% or less as an Al amount from Al203, the ratio of Si and O in case of Sixe2x80x94O is equal to xc2x110% or less as an Si amount from SiO2, or the like. If it is deviated by 10% or more, since optical characteristics change, the modulation degree decreases by 10% or more.
It is preferable that a first protection layer 2 and the material which is substituted for the first protection layer and a second protection layer 3 and the material which is substituted for the second protection layer are 90% or more of the total number of atoms of each protection layer. When an amount of impurities other than the above material is equal to or larger than 10 atom %, deterioration of the rewriting characteristics such that the number of rewriting times decreases to xc2xd or less or the like occurs.
In case of such protection layers, the above effect is obtained when the film thickness of the second protection layer is equal to 2 to 30 nm and the reduction of a recording sensitivity can be suppressed to a value less than 10%, so that it is preferable. It is further preferable if the film thickness is equal to 3 nm or more and is equal to 15 nm or less.
It is desirable that the film thickness of the whole protection layer (the first protection layer and the second protection layer) is equal to 60 to 130 nm because the modulation degree upon recording can be increased to 43% or more and it is more preferable that the film thickness is equal to 80 to 110 nm.
(34) It is characterized in that the first reflection layer is made of Alxe2x80x94Cr. As a material of the first reflection layer in place of Alxe2x80x94Cr, a material such as Alxe2x80x94Ti, Alxe2x80x94Ag, Alxe2x80x94Cu, or the like containing an Al alloy as a main component is preferable because the jitter upon rewriting can be reduced.
It has been found that if a content of the elements except for Al in the Al alloy lies within a range of 5 atom % or more and 30 atom % or less, the characteristics at the time of rewriting of a number of times become excellent. Similar characteristics are obtained even in case of At alloys other than the above alloy.
Subsequently, it is also possible to use a layer made of a sole element such as Au, Ag, Cu, Ni, Fe, Co, Cr, Ti, Pd, Pt, W, Ta, Mo, Sb, Bi, Dy, Cd, Mn, Mg, or V, an alloy containing Au alloy, Ag alloy, Cu alloy, Pd alloy, Pt alloy, Sbxe2x80x94Bi, SUS, Nixe2x80x94Cr, or the like as a main component, or an alloy of them. A multilayer made of those layers can be used. A composite layer of each of those elements and another material such as an oxide, a composite layer of each of those elements and another substance such as another metal, or the like can be used.
Among them, in case of an alloy having a large reflectance such as Cu alloy, Al alloy, Au alloy, or the like, a modulation degree is large and excellent reproducing characteristics are obtained. In case of the Ag alloy and the like, similar characteristics are also derived. If a content of the elements other than the main component in this case is set to a value within a range of 5 atom % or more and 30 atom % or less in a manner similar to that of the Al alloy, the rewriting characteristics are more improved.
(35) It is characterized in that the second reflection layer is made of Alxe2x80x94Ti. As a material of the second reflection layer in place of Alxe2x80x94Ti, a material such as Alxe2x80x94Ag, Alxe2x80x94Cu, Alxe2x80x94Cr, or the like containing an At alloy as a main component is preferable. At can be also used.
It has been found that if a content of the elements except for Al in the Al alloy lies within a range of 0.5 atom % or more and 4 atom % or less, the characteristics at the time of rewriting of a number of times and a bit error rate became preferable and are more preferable when it lies within a range of 1 atom % or more and 2 atom % or less. Similar characteristics are obtained even in case of Al alloys other than the above alloy.
Subsequently, it is also possible to use a layer made of a sole element such as Au, Ag, Cu, Al, Ni, Fe, Co, Cr, Ti, Pd, Pt, W, Ta, Mo, Sb, Bi, Dy, Cd, Mn, Mg, or V, an alloy containing Au alloy, Ag alloy, Cu alloy, Pd alloy, Pt alloy, Sbxe2x80x94Bi, SUS, Nixe2x80x94Cr, or the like as a main component, or an alloy of them. A multilayer made of those layers can be used. A composite layer of each of those elements and another material such as an oxide, a composite layer of each of those elements and another substance such as another metal, or the like can be used.
Among them, in case of a material having a large heat conductivity such as Cu, Al, Au, Cu alloy, Al alloy, Au alloy, or the like, the disk can be easily quenched and excellent rewriting characteristics are obtained. In case of Ag, Ag alloy, and the like, similar characteristics are derived. If a content of the elements other than Cu, Au, Ag, or the like serving as a main component in this case is set to a value within a range of 0.5 atom % or more and 4 atom % or less in a manner similar to the Al alloy, the characteristics upon rewriting of a number of times and a bit error rate are improved and are more improved when it lies within a range of 1 atom % or more and 2 atom % or less.
(36) Refractive indices (n) and attenuation coefficients (k) of the materials of the first and second reflection layers are examined. Thus, if n of the first reflection layer is larger than n of the second reflection layer and k of the first reflection layer is smaller than k of the second reflection layer, the increase in jitter at the time of rewriting of 100,000 times can be suppressed to 4% or less.
It is preferable that the material of each of the first and second reflection layers is equal to or larger than 95% of the total number of atoms of each reflection layer. When an amount of impurities other than the above materials is equal to or larger than 5 atom %, deterioration of the rewriting characteristics such that the number of rewriting times is reduced to xc2xd or less or the like occurs.
When the film thickness of the first reflection layer or the second reflection layer is thinner than 30 nm, since the strength is weak and thermal diffusion is small and the flow of the recording film is likely to occur, the jitter of the front edge or rear edge after completion of the rewriting of 100,000 times increases to a value larger than 12%. When the film thickness is equal to 40 nm, the jitter can be reduced to 10%. When the film thickness of the first reflection layer or the second reflection layer is thicker than 150 nm, a time which is required to manufacture each reflection layer becomes long. The forming time is doubled because the manufacturing step is divided into two or more steps, two or more vacuum chambers for sputtering are provided, or the like. When the film thickness is set to 120 nm or less, since the forming time is shorter than those of the other layers, no influence is exercised on the whole forming time.
Consequently, it is preferable to set the film thickness of the first reflection layer to 30 nm or more and 150 nm or less. It is more preferable to set it to 40 nm to 120 nm. It is preferable to set the film thickness of the second reflection layer to 30 nm or more and 150 nm or less. It is more preferable to set it to 40 nm to 120 nm.
It is desirable to set the film thickness of the whole reflection layer to 60 nm or more and 300 nm or less, more preferably, 80 nm or more and 240 nm or less from a viewpoint of the strength and the forming time in a manner similar to the above. The film thickness of the whole reflection layer is equal to the sum of the film thicknesses of the first and second reflection layers. In the case where either one of the first and second reflection layers does not exist, such a whole film thickness denotes the film thickness of the remaining layer.
(37) Although the materials which have already been mentioned can be used with respect to the materials of the first and second reflection layers, by selecting a combination of them, the increase in jitter at the time of rewriting of 100,000 times can be suppressed to 4% or less and the rewriting characteristics are improved. Preferable combinations are obtained in the case where the main component elements contained in the first and second reflection layers are the same and with respect to the elements other than Al of the main component elements, a content of the second reflection layer is larger than that of the first reflection layer. For example, there are the following cases. The first reflection layer is an Al94Cr6 film and the second reflection layer is Al99Ti1. The first reflection layer is an Al90Ti10film and the second reflection layer is Al98Ti2. The first reflection layer is an Al75Ti25 film and the second reflection layer is Al99Ti1. And the like. Even in case of a combination of Alxe2x80x94Ti and Alxe2x80x94Ti or Alxe2x80x94Cr and Alxe2x80x94Cr, or even in case of combinations other than Alxe2x80x94Ti and Alxe2x80x94Cr, similar characteristics are obtained by using a combination mainly containing an Al alloy such as Alxe2x80x94Ag, Alxe2x80x94Cu, or the like. Subsequently, in case of the Au alloy, Ag alloy, Cu alloy, or compositions close to them, the rewriting characteristics at the time of rewriting of a number of times are improved.
(38) It is characterized that the intermediate layer is made of (ZnS)80(SiO2)20. It is preferable that a mol ratio of ZnS in (ZnS)xe2x80x94(SiO2) of the intermediate layer is equal to 70 mol % or more and is equal to 90 mol % or less. This is because when an amount of ZnS exceeds 90 mol %, noises due to a variation of a crystal grain diameter occur and, when the rewriting is performed 100,000 times, the jitter increases by 4% or more.
In ZnS, a sputtering rate is large and, if an amount of ZnS is large, the film forming time can be reduced, and when 70 mol % or more of the whole intermediate layer consists of ZnS, the film forming time of this layer can be reduced to xc2xd or less.
As a material which is substituted for the intermediate layer, it is possible to use an Sixe2x80x94N system material, an Sixe2x80x94Oxe2x80x94N system material, an oxide such as SiO2, SiO, TiO2, Al2O3, Y2O3, CeO2, La2O3, In2O3, GeO, GeO2, PbO, SnO, SnO2, BeO, Bi2O3, TeO2, WO2, WO3, Sc2O3, Ta2O5, ZrO2, Cu2O, MgO, or the like, a nitride such as TaN, AlN, BN, Si3N4, GeN, Alxe2x80x94Sixe2x80x94N system material (for example, AlSiN2), or the like, a sulfide such as ZnS, Sb2S3, CdS, In2S3, Ga2S3, GeS, SnS2, PbS, Bi2S3, or the like, a selenide such as SnSe2, Sb2Se3, CdSe, ZnSe, In2Se3, Ga2Se3, GeSe, GeSe2, SnSe, PbSe, Bi2Se3, or the like, a fluoride such as CeF3, MgF2, CaF2, or the like, Si, Ge, TiB2, B4C, B, C, or a material made of a composition close to the above materials. A layer of those mixture materials or a multilayer of them can be used.
It is preferable that an element ratio in those compounds is equal to a ratio of a metal element and an oxygen element, for example, in the oxide or sulfide or with respect to the metal element and the sulfide element, it is equal to a ratio of 2:3 in case of Al2O3, Y2O3, and La2O3, 1:2 in case of SiO2, ZrO2, and GeO2, 2:5 in case of Ta2O5, or 1:1 in case of ZnS or a ratio close to it. However, even if the ratio is out of such a ratio, similar effects are obtained. When the ratio is out of the above integer ratio, it is preferable that the deviation of the metal element amount is equal to or less than 10 atom %, namely, for example, the ratio of Al and O in case of Alxe2x80x94O is equal to xc2x110 atom % or less as an Al amount from Al2O3, the ratio of Si and O in case of Sixe2x80x94O is equal to xc2x110 atom % or less as an Si amount from SiO2, or the like. If it is deviated by 10 atom % or more, since optical characteristics change, the modulation degree decreases by 10% or more.
It is preferable that the intermediate layer 5 and the material which is substituted for the intermediate layer 5 are 90% or more of the total number of atoms of each intermediate layer. When an amount of impurities other than the above material is equal to or larger than 10 atom %, deterioration of the rewriting characteristics such that the number of rewriting times decreases to xc2xd or more or the like occurs.
When the film thickness of the intermediate layer is equal to 0 nm, namely, the intermediate layer can be omitted. In this case, since the number of layers is reduced by one, the information recording medium can be easily manufactured. However, diffusion of the reflection layer material into the recording film occurs, the unerased remainder increases, and the jitter at the time of rewriting of 100,000 times exceeds 13%. When the film thickness is thinner than 10 nm, the recording sensitivity decreases by 5% or more. Further, to suppress the flow of the recording film, it is preferable to set the film thickness to 40 nm or less. The jitter of the rear edge at the time of rewriting of 100,000 times can be suppressed to 13% or less. When the film thickness is equal to or less than 30 nm, the jitter can be suppressed to 10% or less. Thus, if the film thickness of the intermediate layer is set to 10 to 30 nm, the recording and reproducing characteristics are more improved and it is preferable.
(39) It is characterized in that the substrate is made of a polycarbonate substrate directly having a tracking groove on the surface. In place of it, it is possible to use a chemical strengthening glass or the like in which polyolefin, epoxy, acrylate resin, or ultraviolet hardening resin layer has been formed on the surface.
The substrate having the tracking groove is a substrate having a groove whose depth is equal to xcex/10nxe2x80x2 (nxe2x80x2 is a refractive index of the substrate material) or more on all of or a part of the substrate surface when a recording/reproducing wavelength is set to xcex. The groove can be continuously formed by one circumference or can be divided on the halfway. A width of groove can be different in dependence on the location. It is also possible to use a substrate of a sampling servo format on which no groove portion exists, a substrate by another tracking system, a substrate by another format, or the like. It is also possible to use a substrate having a format in which the recording and reproduction can be performed to both groove portion and land portion or a substrate of a format in which the recording is performed to either of them. A disk size is not limited to 12 cm but can be set to any other size such as 13 cm, 3.5xe2x80x2, 2.5xe2x80x2, or the like. A thickness of disk is also not limited to 0.6 mm but can be set to any other thickness such as 1.2 mm, 0.8 mm, or the like.
In the information recording medium, two disk members are formed and second reflection layers 7 and 7xe2x80x2 of the first and second disk members are adhered through an adhesive layer. However, in place of the second disk member, a disk member of another construction, a substrate for protection, or the like can be used. When a transmittance in a ultraviolet wavelength region of the disk members which are used for adhesion or the substrate for protection is large, the disk members can be adhered by the ultraviolet hardening resin. They can be adhered by another method.
In the information recording medium, two disk members are formed and the second reflection layers 7 and 7xe2x80x2 of the first and second disk members are adhered through an adhesive layer. However, if the ultraviolet hardening resin of a thickness of about 10 xcexcm is coated onto the second reflection layers 7 and 7xe2x80x2 of the first and second disk members prior to adhering and the disk members are adhered after the ultraviolet hardening resin was hardened, an error rate can be further reduced. Although the recording and reproducing characteristics and the like are improved even by merely setting each of the film thickness and the material of each layer into a sole preferable range, by combining the preferable ranges, the effect is further raised.
(40) It is characterized in that the recording film is made of Agxe2x80x94Gexe2x80x94Sbxe2x80x94Te.
It is preferable to set the range of z to 0xe2x89xa6zxe2x89xa60.06 and a range showing more excellent characteristics is set to 0xe2x89xa6zxe2x89xa60.04.
As an element which is added into the recording film in place of Ag, it has been found that it is difficult to increase the jitter at the time of rewriting of a number of times even if it is replaced with at least any one of
Na, Mg, Al, P, S, Cl, K, Ca, Sc, Zn, Ga, As, Se, Br, Rb, Sr, Y, Zr, Nb, Ru, Rh, Cd, In, Sn, I, Cs, Ba, La, Hf, Ta, Re, Os, Ir, Hg, Tl, Pb, Th, U, Cr, W, Mo, Pt, Co, Ni, Pd, Si, Au, Cu, V, Mn, Fe, Ti, and Bi.
There are effects such that among them, particularly, when Ag is added, the recording sensitivity is also improved by 10% as compared with that in case of Gexe2x80x94Sbxe2x80x94Te, when at least any one of Cr, W, and Mo is added, the jitter increases by 5% or more and the number of rewriting times is improved by three times or more when the rewriting is performed a number of times as compared with those in case of Gexe2x80x94Sbxe2x80x94Te, and when at least any one of Pt, Co, and Pd is added, the crystallization temperature rises by 50xc2x0 C. or more as compared with that in case of Gexe2x80x94Sbxe2x80x94Te.
(41) It is characterized in that the first protection layer is made of (Al2O3)70(ZnS)10(SiO2)20.
It is preferable that 70 atom % or more of the total number of atoms of the protection layer component is Alxe2x80x94O because the reduction of the reflectance level can be suppressed to 5% or less. In ZnS, a sputtering rate is large and, if an amount of ZnS is large, the film forming time can be reduced, and when 70 mol % or more of the whole protection layer consists of ZnS, the film forming time of the protection layer can be reduced to xc2xd or less.
As a material which is substituted for Al2O3 in the (Al2O3)70(ZnS)10(SiO2)20 mixture material, SiO2 or a mixture material of Al2O3 and SiO2 is preferable. Ta2O5 is subsequently preferable and ZrO2xe2x80x94Y2O3 or a mixture material of them and Al2O3 and SiO2 is subsequently preferable.
In place of Al2O3 of the second protection layer, if a Crxe2x80x94O system material such as Cr2O3, CrO, or the like, a Coxe2x80x94O system material such as Co2O3, CoO, or the like, a material of a composition close to them, or a mixture material of them is used, it is preferable because an adhesive strength between the protection layer and the recording film is strong.
As a material which is substituted for (ZnS)30(SiO2)20, it is possible to use a material in which a mixture ratio of ZnS and SiO2 is changed, an Sixe2x80x94N system material, an Sixe2x80x94Oxe2x80x94N system material, an oxide such as SiO2, SiO, TiO2, Al2O3, Y2O3, CeO2, La2O3, In2O3, GeO, GeO2, PbO, SnO, SnO2, BeO, Bi2O3, TeO2, WO2, WO3, Sc2O3, Ta2O5, ZrO2, Cu2O, MgO, or the like, a nitride such as TaN, AlN, BN, Si3N4. GeN, Alxe2x80x94Sixe2x80x94N system material (for example, AlSiN2), or the like, a sulfide such as ZnS, Sb2S3, CdS, In2S3, Ga2S3, GeS, SnS2, PbS, Bi2S3. or the like, a selenide such as SnSe2, Sb2Se3, CdSe, ZnSe, In2Se3, Ga2Se3, GeSe, GeSe2, SnSe, PbSe, Bi2Se3l or the like, a fluoride such as CeF3, MgF2, CaF2, or the like, Si, Ge, TiB2, B4C, B, C, or a material made of a composition close to the above materials. A layer of those mixture materials or a multilayer of them can be used.
In case of such a protection layer, it is preferable to set the film thickness of the whole protection layer to 80 to 110 nm because a modulation degree upon recording can be increased.
(42) It is characterized in that the first reflection layer is made of Alxe2x80x94Ti. As a material of the first reflection layer in place of Alxe2x80x94Ti, a material mainly containing an Al alloy such as Alxe2x80x94Cr, Alxe2x80x94Ag, Alxe2x80x94Cu, or the like is preferable.
In case of the Al alloy, if a content of the elements other than Al in the Al alloy is set to a value within a range of 5 atom % or more and 30 atom % or less, the characteristics at the time of rewriting of a number of times are further improved. Similar characteristics are obtained even in case of Al alloys other than those mentioned above.
Subsequently, it is also possible to use a layer made of a sole element such as Au, Ag, Cu, Al, Ni, Fe, Co, Cr, Ti, Pd, Pt, W, Ta, Mo, Sb, Bi, Dy, Cd, Mn, Mg, or V, an alloy containing Au alloy, Ag alloy, Cu alloy, Pd alloy, Pt alloy, Sbxe2x80x94Bi, SUS, Nixe2x80x94Cr, or the like as a main component, or an alloy of them. A multilayer made of those layers can be used. A composite layer of each of those elements and another material such as an oxide, a composite layer of each of those elements and another substance such as another metal, or the like can be used.
Among them, in case of a material having a large reflectance such as Cu alloy, Al alloy, Au alloy, or the like, a modulation degree is large and excellent reproducing characteristics are obtained. Similar characteristics are also obtained in case of the Ag alloy or the like. If a content of the elements other than the main component such as Cu, Au, Ag, or the like serving as a main component in this case is set to a value within a range of 5 atom % or more and 30 atom % or less, the characteristics are further improved.
Although the materials which have already been mentioned can be used with respect to the combinations of the materials of the first and second reflection layers, it has been found that by selecting the combination of them, the increase in jitter at the time of rewriting of 100,000 times can be suppressed to 4% or less and the rewriting characteristics are improved. Preferable combinations are obtained in the case where the main component elements contained in the first and second reflection layers are the same and with respect to the elements other than Al of the main component elements, a content of the second reflection layer is larger than that of the first reflection layer. For example, there are the following cases. The first reflection layer is an Al94Cr6 film and the second reflection layer is Al99Ti1. The first reflection layer is an Al90Ti10 film and the second reflection layer is Al98Ti2. The first reflection layer is an Al75Ti25 film and the second reflection layer is Al99Ti1. And the like. Even in case of a combination of Alxe2x80x94Ti and Alxe2x80x94Ti or Alxe2x80x94Cr and Alxe2x80x94Cr, or even in case of combinations other than Alxe2x80x94Ti and Alxe2x80x94Cr, similar characteristics are obtained by using a combination mainly containing an Al alloy such as Alxe2x80x94Ag, Alxe2x80x94Cu, or the like. Subsequently, in case of the Au alloy, Ag alloy, Cu alloy, or compositions close to them, the rewriting characteristics at the time of rewriting of a number of times are improved.
Among them, in the case where the elements other than the main component are the same as shown in the combination in which the first reflection layer is an Al90Ti10 film and the second reflection layer is Al98Ti2, since the heat is likely to escape from the recording film to the reflection layer, in the jitter after completion of rewriting of 10 times, a recording power margin in which both the jitter of the front edge and the jitter of the rear edge decrease is widened by 5%.
(43) It is characterized in that the first protection layer is made of Al2O3 and (ZnS)80(SiO2)20 and the second protection layer 3 is made of Al2O3.
It is preferable that a mol ratio of ZnS in (ZnS)xe2x80x94(SiO2) of the first protection layer 2 is equal to 70 mol % or more and is equal to 90 mol % or less.
As a material which is substituted for (ZnS)80(SiO2)20 of the first protection layer 2, it is possible to use an Sixe2x80x94N system material, an Sixe2x80x94Oxe2x80x94N system material, an oxide such as SiO2, SiO, TiO2, Al2O3, Y2O3, CeO2, La2O3, In2O3, GeO, GeO2, PbO, SnO, SnO2, BeO, Bi2O3, TeO2, WO2, WO3, Sc2O3, Ta2O5, ZrO2, Cu2O, MgO, or the like, a nitride such as TaN, AlN, BN, Si3N4, GeN, Alxe2x80x94Sixe2x80x94N system material (for example, AlSiN2), or the like, a sulfide such as ZnS, Sb2S3, CdS, In2S3, Ga2S3, GeS, SnS2, PbS, Bi2S3, or the like, a selenide such as SnSe2, Sb2Se3l CdSe, ZnSe, In2Se3, Ga2Se3, GeSe, GeSe2, SnSe, PbSe, Bi2Se3l or the like, a fluoride such as CeF3, MgF2, CaF2, or the like, Si, Ge, TiB2, B4C, B, C, or a material made of a composition close to the above materials. A layer of those mixture materials or a multilayer of them can be used.
As a material which is substituted for Al2O3 of the first protection layer 2, MgO, BeO, AlN, BN, or B4C is preferable. Subsequently, Ta2O5, SiO2, ThO2, TiO2, or SiC is preferable.
When the film thickness of this layer is set to 5 nm or more, the reflectance level change at the time of rewriting of 100,000 times can be suppressed to 10% or less. If it is set to 20 nm or more, the reflectance level change at the time of rewriting of 100,000 times can be suppressed to 5% or less. Further, if it is set to 70 nm or more, the forming time of the protection layer becomes long and the forming time is doubled because the manufacturing step is divided into two or more steps, two or more vacuum chambers for sputtering are provided, or the like. When the film thickness is set to 50 nm or less, since the forming time of the layer is shorter than those of the other layers, no influence is exercised on the whole forming time. It is, consequently, desirable to set the film thickness to 5 to 70 nm, more preferably, 20 to 50 nm.
As a material which is substituted for Al2O3 of the second protection layer 3, SiO2 or a material in which a mixture ratio of Al2O3 and SiO2 is changed is preferable. Subsequently, Ta2O5 is preferable. ZrO2xe2x80x94Y2O3 is subsequently preferable.
It is preferable that an element ratio in those compounds is equal to a ratio of a metal element and an oxygen element, for example, in the oxide or sulfide or with respect to the metal element and the sulfide element, it is equal to a ratio of 2:3 in case of Al2O3, Y2O3, and La2O3, 1:2 in case of SiO2, ZrO2, and GeO2, 2:5 in case of Ta2O5, or 1:1 in case of ZnS or a ratio close to it. However, even if the ratio is out of such a ratio, similar effects are obtained. When the ratio is out of the above integer ratio, it is preferable that the deviation of the metal element amount is equal to or less than 10 atom %, namely, for example, the ratio of Al and O in case of Alxe2x80x94O is equal to xc2x110 atom % or less as an Al amount from Al2O3, the ratio of Si and O in case of Sixe2x80x94O is equal to xc2x110 atom % or less as an Si amount from SiO2, or the like. If it is deviated by 10 atom % or more, since optical characteristics change, the modulation degree decreases by 10% or more.
In place of Al2O3 of the second protection layer, if a Crxe2x80x94O system material such as Cr2O3, CrO, or the like, a Coxe2x80x94O system material such as Co2O3, CoO, or the like, a material of a composition close to them, or a mixture material of them is used, it is preferable because an adhesive strength between the protection layer and the recording film is strong. Or, an Nixe2x80x94O system material or a mixture material of them can be used.
It is desirable to use a nitride such as Gexe2x80x94N, Sixe2x80x94N, or Alxe2x80x94N system material other than them because there is an effect such that the crystallization speed rises and the unerased remainder decreases at the high linear velocity. Even in case of forming the layer by adding nitrogen into the recording film material, the crystallization speed also rises.
In case of such a protection layer, it is preferable to set the film thickness of the second protection layer to 2 to 30 nm because the reduction of the recording sensitivity can be set to 10% or less and the forming time can be reduced. It is more preferable to set the film thickness to 3 nm or more and 15 nm or less. It is desirable to set the film thickness of the whole protection layer to 80 to 110 nm because the modulation degree upon recording can be increased.
(44) It is characterized in that the intermediate layer is made of two layers of Al2O3 and (ZnS)80(SiO2)20. As a material which is substituted for Al2O3, SiO2 or Al2O3xe2x80x94SiO2 can be used. When it is changed to SiO2, as compared with the case of Al2O3, although an increasing degree of the jitter at the time of rewriting of a number of times increases, even if the linear velocity upon recording is raised to about 1.5 times, a DC erasing ratio can be held to 30 dB or more. If SiO2 or Al2O3 of an amount corresponding to 70 atom % or more is contained, the reduction of the reflectance level due to the rewriting of 100,000 times can be suppressed to 5% or less. When 90 atom % or more is contained, the reflectance level reduction can be suppressed to 3% or less. In place of Al2O3, Ta2O5 is subsequently preferable and ZrO2xe2x80x94Y2O3 is subsequently preferable.
In place of Al2O3 of the intermediate layer, if a Crxe2x80x94O system material such as Cr2O3, CrO, or the like, a Coxe2x80x94O system material such as Co2O3, CoO, or the like, a material of a composition close to them, or a mixture material of them is used, it is preferable because an adhesive strength between the protection layer and the recording film is strong. Or, an Nixe2x80x94O system material or a mixture material of them can be used.
It is desirable to use a nitride such as Gexe2x80x94N, Sixe2x80x94N, or Alxe2x80x94N system material other than them because there is an effect such that the crystallization speed rises and the unerased remainder decreases at the high linear velocity. Even in case of forming the layer by adding nitrogen into the recording film material, the crystallization speed also rises.
In the case where there is Al2O3 or a layer which is substituted for it, there is an effect of preventing that (ZnS)80(SiO2)20 of the intermediate layer or a material which is substituted for it is diffused. The reduction of the reflectance level due to the rewriting of 100,000 times can be suppressed to 1% or less. In the case where the intermediate layer is made of only Al2O3 or a layer which is substituted for it, the recording sensitivity decreases by 5%. Therefore, when the intermediate layer is made of two or more layers of different materials, although the number of manufacturing steps increases, since there are both effects such that an increase in noises is prevented and the diffusion of the protection layer material into the recording film is prevented, it is preferable.
As a combination of the intermediate layer on the reflection layer side and the intermediate layer on the recording film side, in case of (ZnS)80(SiO2)20 and Al2O3, the reflectance level change upon rewriting is small to be 1% or less and it is preferable. In case of (ZnS)80(SiO2)20 and SiO2, a DC erasing ratio is equal to 30 dB and excellent erasing characteristics are obtained. A combination of ZnS and any one of SiO2, Al2O3, and Ta2O5 is preferable because a modulation degree is large to be 53% or more.
In place of using two layers of Al2O3 or a material which is substituted for Al2O3 and (ZnS)80(SiO2)20 or a material which is substituted for (ZnS)80(SiO2)20, if a mixture of both of them is used, although the erasing characteristics at a high linear velocity are worse as compared with those in case of using two layers, the film forming time can be reduced. In this instance, in case of (ZnS)xe2x80x94(Al2O3)xe2x80x94(SiO2), when the linear velocity is raised by 1.1 times, the erasing ratio is equal to 30 dB or more and the film forming time is reduced to about xc2xd because one layer is formed. Since the erasing ratio is large, it is more preferable. If an amount of Alxe2x80x94O in the intermediate layer is set to 70 atom % or more of the total number of atoms, since the reflectance level change at the time of rewriting of a number of times can be reduced to 5% or less, it is more desirable.
It is preferable that a mol ratio of ZnS in (ZnS)xe2x80x94(SiO2) of the intermediate layer 5 is equal to 70 mol % or more and is equal to 90 mol % or less. This is because when ZnS exceeds 90 mol %, noises due to a variation in crystal grain diameter occur and, when the rewriting is performed 100,000 times, the jitter increases by 4% or more.
In ZnS, a sputtering rate is large and, if an amount of ZnS is large, the film forming time can be reduced, and when 70 mol % or more of the whole intermediate layer consists of ZnS, the film forming time of this layer can be reduced to xc2xd or less.
As a material which is substituted for (ZnS)xe2x80x94(SiO2) of the intermediate layer 5, it is possible to use an Sixe2x80x94N system material, an Sixe2x80x94Oxe2x80x94N system material, an oxide such as SiO2, SiO, TiO2, Al2O3, Y2O3, CeO2, La2O3, In2O3, GeO, GeO2, PbO, SnO, SnO2, BeO, Bi2O3, TeO2, WO2, WO3, Sc2O3, Ta2O5, ZrO2, Cu2O, MgO, or the like, a nitride such as TaN, AlN, BN, Si3N4, GeN, Alxe2x80x94Sixe2x80x94N system material (for example, AlSiN2), or the like, a sulfide such as ZnS, Sb2S3, CdS, In2S3, Ga2S3, GeS, SnS2, PbS, Bi2S3, or the like, a selenide such as SnSe2, Sb2Se3, CdSe, ZnSe, In2Se3, Ga2Se3, GeSe, GeSe2, SnSe, PbSe, Bi2Se3, or the like, a fluoride such as CeF3, MgF2, CaF2, or the like, Si, Ge, TiB2, B4C, B, C, or a material made of a composition close to the above materials. A layer of those mixture materials or a multilayer of them can be used.
It is preferable that an element ratio in those compounds is equal to a ratio of a metal element and an oxygen element, for example, in the oxide or sulfide or with respect to the metal element and the sulfide element, it is equal to a ratio of 2:3 in case of Al2O3, Y2O3, and La2O3, 1:2 in case of SiO2, ZrO2, and GeO2, 2:5 in case of Ta2O5, or 1:1 in case of ZnS or a ratio close to it. However, even if the ratio is out of such a ratio, similar effects are obtained. When the ratio is out of the above integer ratio, it is preferable that the deviation of the metal element amount is equal to or less than 10%, namely, for example, the ratio of Al and O in case of Alxe2x80x94O is equal to xc2x110% or less as an Al amount from Al2O3, the ratio of Si and O in case of Sixe2x80x94O is equal to xc2x110% or less as an Si amount from SiO2, or the like. If it is deviated by 10% or more, since optical characteristics change, the modulation degree decreases by 10% or more.
It is preferable that the intermediate layer 5 and the material which is substituted for the intermediate layer 5 are 90% or more of the total number of atoms of each intermediate layer. When an amount of impurities other than the above material is equal to or larger than 10 atom %, deterioration of the rewriting characteristics such that the number of rewriting times decreases to xc2xd or more or the like occurs.
When the film thickness of the whole intermediate layer is thinner than 10 nm, the recording sensitivity decreases by 5% or more. It is further desirable to set the film thickness to 40 nm or less in order to suppress the flow of the recording film. The jitter of the rear edge at the time of rewriting of 100,000 times can be suppressed to 13% or less. When the film thickness is equal to 30 nm or less, the jitter can be suppressed to 10% or less. Consequently, it is preferable to set the film thickness of the intermediate layer to 10 to 30 nm because the recording and reproducing characteristics are further improved.
(45) It is characterized in that the first reflection layer is made of Si. As a material of the first reflection layer in place of Si, if Au, Ag, Cu, Al, Ni, Fe, Co, Cr, Ti, Pd, Pt, W, Ta, Mo, Sb, Bi, Dy, Cd, Mn, Mg, V, Zn, Ga, Tl, Pb, C, B, S, or Ge is added into Si, a transmittance of the reflection layer decreases and an absorptance rises, so that the deterioration of the sensitivity can be prevented. In this case, if an amount of Si in the first reflection layer is equal to 80 atom % or less, the absorptance is excessively large and that if the linear velocity is raised up to 1.5 times, an increasing rate of the jitter exceeds 4%.
Among them, a material of Sixe2x80x94Mo or Sixe2x80x94Al as well as Sixe2x80x94Ti is more preferable because a heat conductivity of the first reflection layer can be raised and an optical constant can be set to a proper value. As for an addition amount of the element which is added into Si, it has been found that an amount within a range of 2 atom % or more and 10 atom % or less is more preferable because the reflectance level change at the time of rewriting of a number of times can be reduced to 10% or less and it is particularly desirable to set the addition amount to 3 to 6 atom %.
It is preferable that an amount of material of the first reflection layer is equal to or larger than 95% of the total number of atoms of each reflection layer. When an amount of impurities other than the above materials is equal to 5 atom % or more, there is a deterioration of the rewriting characteristics such that the number of rewriting times is reduced to xc2xd or less, or the like.
By adding Ti, Mo, Al, or the like into Si, the change in reflectance due to the wavelength decreases. Thus, even when the wavelength upon initialization and the recording/reproducing wavelength are different, since an initializing power can be set to a high sensitivity, it is preferable. Even when the recording wavelength and the reproducing wavelength differ, similarly, since a recording power or a reproducing power can be easily reduced, it is preferable. In case of the Sixe2x80x94Ge system material, since a light absorptance of the recording mark portion can be set to be smaller than that of the portion other than the recording mark, the unerased remainder due to a difference of the light absorptance can be prevented and, further, the number of rewriting times is not reduced.
As another material of the first reflection layer, a sulfide such as Cdxe2x80x94S, Inxe2x80x94Se, or the like or a selenide such as Znxe2x80x94Se, Cdxe2x80x94Se, Inxe2x80x94Se, or the like can be used. It is desirable to set a refractive index to 3 or more. However, since the heat conductivity is low, an increase degree of the jitter due to the rewriting of 100,000 times is large.